Well I mean SONY still has a few of them. Nihilistic, Sanzaru, Novarama, Mass Media.,Clap Hanz, etc. They may have ended their relationship with Idol Minds and High Impact, but it seems they still have eligible candidates to fit the bill. I don't think that SCE as a publisher has faith in that type of investment though. Which enulls any of the above possibilities.
I would have thought that SCE could survive the platform on more PS3/PSVita cross-platform stuff. Or more PS2/PS3 classics ported to the system. As you mentioned, a Gran Turismo Vita or Gran Turismo 6-Vita would have been absolutely key here. Even if it failed to do anything, how can SCE not push their biggest selling IP on the platform.
Going as far back as launch, I think SCE was delusional about always pushing Wipeout as the premiere second first-party launch title. GT and Uncharted together would have been a great killer start. But looking at the PS4 launch, I don't think they excel at coordinating launch software.